114 ME. GAKDIKEE AND PBOF. EEYJSTOLDS 0]S T THE [June 1 9 1 4, 



the felsite, but possibly also the apparent thickness of the bostonite 

 which may be swung round by the fault. As the big felsite-niass 

 south of Curraghrevagh hamlet is unaffected by this fault, it is 

 probably a post- Silurian intrusion. 



Taking the Lough Nafooey and Kilbride areas together, the 

 bostonite -sill has been traced almost continuously for a distance 

 of 7 miles. How much farther it extends is unknown, but it is 

 seen on the northern shore of Deny Bay, half a mile from its 

 outcrop at the eastern end of the Kilbride peninsula. 



A second considerable intrusion of lime-bostonite occurs as a 

 dyke in the spilite to the south-west of the top of Bencorragh, 

 having a length of about three-quarters of a mile. The eastern 

 part lies parallel to the main sill ; but the western part diverges 



Fig. 3. 



-Section in Stream B, flowing cloivn from Benbeg 

 to Curraglirevagli hamlet. 



a^Recl Sandstone. 

 b = Conglomerate. 



[Scale : 1 inch = about 100 feet.] 



c— Patches of black pyritous shale. e= Gritty rock. 

 d= Bostonite. f= Fault. 



northwards, and is penetrated by two small dolerite-dykes. North 

 of the little tarn at the col between the Bencorragh and Curragh- 

 revagh ridges, two smaller intrusions in spilite occur, trending 

 respectively a little to the east and a little to the west of north. 



(d) The Dolerites. 



The dolerite-intrusions include (a) augite-dolerites devoid of 

 mica, and (b) mica-dolerites. 



The augite-dolerites occur as dykes in the spilites. They tend 

 to weather to the same dark -brown colour as the spilites, and are 

 in consequence often difficult to recognize in the field. 



In the Kilbride area mica-dolerites were generally found intrusive 

 in the Finny School Beds. In the Lough Nafooey area they 

 mainly occur in the overlying Purple Sandy Shale. For the first 



